Washington State University Puyallup
  Organic Farming Systems and Nutrient Management

Calculating Compost Bulk Density

 

Materials Needed:

1. Compost pile
2. 5-gallon bucket
    (straight sides preferred)
3. Permanent pen 
    marker
4. Gallon measuring
    container
5. Scale (pounds)
6. Ruler

Bulk Density Bucket Bulk Density Bucket 2

Procedure:

  1. With a 1-gallon measuring container, fill 5-gallon bucket with 5 gallons of water as the brim of a "5 gallon bucket" is not necessarily 5 gallons.  Mark this line on at least 3 places on the inside of the bucket with a permanent pen.

  2. a) Buckets with straight sides (ie diameter at the top of the bucket is the same as the diameter at the bottom): measure height from bottom of inside of bucket to the 5 gallon line, divide this number by 3, and mark the bucket as above at 1 times and 2 times this number.  For example, if the 5-gallon mark is 13 inches, dividing by 3 will get 4.33 inches, so mark that bucket at 4.33 inches and 8.67 inches. 
    b) If you cannot obtain a bucket with straight sides: find the two intermediate lines by measuring first 1 2/3 gallons (=1.67 gal or 6.31 liters) then 3 1/3 gallons (=3.33 gallons or 12.62 liters) of water into the bucket and marking where the water line is at both volumes with a pencil when wet, then a permanent pen when dry.

  3. Compost used should be representative of the pile.  Take handful samples (not large shovel full samples) from several locations in the pile.  Dig into pile a couple of feet, do not take from dried-out outer layer of pile.  

  4. Fill bucket to the 1/3 line with compost. Drop bucket squarely from approximately 1 foot high to the ground (hard surface) 10 times.  

  5. Fill bucket to the 2/3 line.  Drop bucket squarely from approximately 1 foot high to the ground 10 times.

  6. Fill bucket to the 3/3 (5 gallon) line.  Drop bucket squarely from approximately 1 foot high to the ground 10 times.

  7. Fill bucket again to the 3/3 (5 gallon) line and weigh in pounds.

  8. Multiply weight of material in pounds (excluding bucket weight) by 40.  
    This is your bulk density, in pounds per cubic yard.

 

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